1. Field
The present invention concerns ultraviolet (“UV”) barrier films, in particular polymeric films comprising a mixture of both inorganic and organic UV blocking compounds.
2. Description of the Related Art
UV barrier films are well known in the art. Thus, WO-A-04/87795 discloses a biaxially oriented polypropylene (BOPP) film which has dispersed therein rigid rod like UV absorbers compatible with the polymer such as (E,E)-1,4-diphenylbuta-1,3-diene (DPBD); (E,E)-1,6-diphenylhexa-1,3,5-triene (DPHT); and beta, beta-carotene (carotene) at typical concentrations of about 0.01% w/w. These absorbers preferentially align along one of the two orientation axes of the film and allow anisotropy in the film to be covertly detected by the difference in the UV fluorescence spectra of the film in along each axis. This provides a covert means to authenticate the film, which is useful as a substrate for security applications.
EP-B-1004626 discloses a thin packaging film made out of a thermoplastic material with anti-UV properties, characterized in that its composition further comprises a combination of at least one organic compound with at least one inorganic UV-absorbent compound, for improved barrier against UV rays, and improved transparency. Preferably, the organic compound is a benzotriazole, and the inorganic compound is micronized zinc oxide. More preferably, the material for the film further comprises a binder compound, for example a benzophenone, in order to improve the compatibility between the organic component and the base-resin.
EP-A-160981 discloses a polymer composition which is used as a masterbatch comprising polyolefin and 10 to 80 wt-% nano scalar zinc oxide having a particle size between 1 and 100 nm. The invention further relates to a film made from this masterbatch and to a method for manufacturing said film.
U.S. Pat. No. 6,916,867 discloses polyolefin compositions which comprise as UV absorber a synergistic mixture of a) at least one hydroxybenzophenone and at least one 2-hydroxyphenylbenzotriazole with the proviso that the polyolefin is a high density polyethylene of the “Phillips” type or a polyethylene of the metallocene type; b) at least one hydroxybenzophenone and at least one 2-hydroxyphenyltriazine, with the proviso that if the polyolefin is polypropylene, no polyvinylpyridin is present c) at least one hydroxybenzophenone and at least one oxanilide; d) at least one 2-hydroxyphenylbenzotriazole and at least one oxanilide; e) at least one 2-hydroxyphenyltriazine and at least one oxanilide; f) at least one hydroxybenzophenone, at least one 2-hydroxyphenylbenzotriazole and at least one oxanilide; g) at least one hydroxybenzophenone, at least one oxanilide and at least one 2-hydroxyphenyltriazine; or h) at least one 2-hydroxyphenylbenzotriazole, at least one oxanilide and at least one 2-hydroxy phenyltriazine.